Autonomous driving system

ABSTRACT

An autonomous driving system mounted on a vehicle determines a target path based on necessary information and performs vehicle travel control such that the vehicle follows the target path. A first coordinate system is a vehicle coordinate system at a first timing when the necessary information is acquired. A second coordinate system is a vehicle coordinate system at a second timing later than the first timing. The autonomous driving system calculates, based on the necessary information acquired at the first timing, a first target path defined in the first coordinate system. Then, the autonomous driving system corrects the first target path to a second target path defined in the second coordinate system by performing coordinate transformation from the first coordinate system to the second coordinate system. The autonomous driving system uses the second target path as the target path to perform the vehicle travel control.

The present application is a continuation of U.S. application Ser. No.17/522,053, filed on Nov. 9, 2021, which is a continuation of U.S.application Ser. No. 16/851,613, filed on Apr. 17, 2020, which is acontinuation of U.S. application Ser. No. 15/899,822, filed on Feb. 20,2018, which claims priority to Japanese Application 2017-082894, filedon Apr. 19, 2017, the disclosures of each of which are herebyincorporated by reference.

BACKGROUND Technical Field

The present disclosure relates to an autonomous driving system. Inparticular, the present disclosure relates to an autonomous drivingsystem that controls travel of a vehicle to follow a target path.

Background Art

Patent Literature 1 discloses a vehicle travel support device thatsupports travel of a vehicle. The vehicle travel support devicecalculates a control command value for avoiding an obstacle, based onvehicle motion state and obstacle state detected by sensors. Morespecifically, the vehicle travel support device calculates both alow-precision first control command value and a high-precision secondcontrol command value. A time required for calculating thehigh-precision second control command value is longer than a timerequired for calculating the low-precision first control command value.That is, calculation delay occurs when calculating the second controlcommand value. In order to compensate for such the calculation delay,the vehicle travel support device uses the vehicle motion state and theobstacle state detected by the sensors to “predict” future vehiclemotion state and obstacle state the calculation delay time after. Then,the vehicle travel support device calculates the high-precision secondcontrol command value based on the predicted future vehicle motion stateand obstacle state.

Patent Literature 2 discloses an autonomous driving system. Theautonomous driving system has: a surrounding information detection unitthat detects surrounding information of a vehicle; a travel plangeneration unit that generates a travel plan of the vehicle based on thedetected surrounding information and map information; and a travelcontrol unit that autonomously controls travel of the vehicle accordingto the generated travel plan.

LIST OF RELATED ART

-   Patent Literature 1: Japanese Laid-Open Patent Publication No.    2010-173616-   Patent Literature 2: Japanese Laid-Open Patent Publication No.    2016-099713

SUMMARY

Let us consider “path-following control” performed by an autonomousdriving system. In the path-following control, the autonomous drivingsystem periodically calculates a target path for a vehicle, and controlstravel of the vehicle so as to follow the latest target path. In thepath-following control, control delay may occur due to various factors.

For example, one factor for the control delay is a calculation timerequired for calculating the target path. Information necessary forcalculating the target path is acquired at a predetermined timing, andthe calculation of the target path based on the acquired information iscompleted after the predetermined timing. Such the calculation timerequired for calculating the target path causes the control delay.

The control delay of the path-following control causes decrease inperformance of following the target path. When the path-followingperformance of the autonomous driving system is decreased, an occupantof the vehicle feels senses of anxiety and strangeness, which leads todecrease in confidence in the autonomous driving system.

According to the technique disclosed in the above-mentioned PatentLiterature 1, the calculation delay is taken into consideration whencalculating the high-precision second control command value. Morespecifically, the vehicle motion state and the obstacle state detectedby the sensors are used to “predict” future vehicle motion state andobstacle state the calculation delay time after. Then, thehigh-precision second control command value is calculated based on thepredicted future vehicle motion state and obstacle state. However,predicting the vehicle motion state and the obstacle state requirescomplicated computation processing, which causes increase in computationload, computation time, and computational resource.

An object of the present disclosure is to provide a technique that canincrease path-following performance with suppressing increase incomputation load, in an autonomous driving system that controls travelof a vehicle so as to follow a target path.

A first disclosure provides an autonomous driving system mounted on avehicle.

The autonomous driving system includes:

a necessary information acquisition unit periodically acquiringnecessary information that is necessary for calculating a target path;

a target path determination unit determining the target path based onthe necessary information; and

a vehicle travel control unit performing vehicle travel control thatcontrols travel of the vehicle so as to follow the target path.

A vehicle coordinate system is a relative coordinate system fixed to thevehicle.

A first timing is a timing when the necessary information acquisitionunit acquires the necessary information.

A first coordinate system is the vehicle coordinate system at the firsttiming.

A second coordinate system is the vehicle coordinate system at a secondtiming later than the first timing.

The target path determination unit includes:

a target path calculation unit calculating, based on the necessaryinformation acquired at the first timing, a first target path defined inthe first coordinate system; and

a target path correction unit correcting the first target path to asecond target path defined in the second coordinate system by performingcoordinate transformation from the first coordinate system to the secondcoordinate system.

The vehicle travel control unit uses the second target path as thetarget path to perform the vehicle travel control.

A second disclosure further has the following features in addition tothe first disclosure.

A delay time from the first timing to the second timing ispredetermined.

A third disclosure further has the following features in addition to thefirst or second disclosure.

A delay time from the first timing to the second timing corresponds to atime required for the target path calculation unit to calculate thefirst target path.

A fourth disclosure further has the following features in addition tothe third disclosure.

The target path determination unit determines and updates the targetpath every time the necessary information acquisition unit acquires thenecessary information.

The target path determination unit determines a new target path suchthat a certain section from beginning of the new target path overlaps aprevious target path.

The certain section includes at least a section corresponding to aperiod from the first timing to the second timing.

According to the first disclosure, the autonomous driving systemperforms target path correction processing in the path-followingcontrol. More specifically, the autonomous driving system corrects thefirst target path defined in the first coordinate system to the secondtarget path defined in the second coordinate system. The firstcoordinate system is the vehicle coordinate system at the first timingwhen the necessary information is acquired. The second coordinate systemis the vehicle coordinate system at the second timing later than thefirst timing. Influence of the control delay is reduced by the targetpath correction processing. Therefore, when the second target path afterthe correction is used to perform the vehicle travel control, controlerror becomes smaller and control accuracy becomes higher as comparedwith a case where the first target path is used. In other words, theperformance of following the target path is increased. When thepath-following performance of the autonomous driving system isincreased, the senses of anxiety and strangeness of the vehicle occupantare reduced, which contributes to increase in confidence in theautonomous driving system.

Moreover, complicated computation processing is unnecessary for thetarget path correction processing. It is possible to easily obtain thesecond target path by performing simple coordinate transformation fromthe first coordinate system to the second coordinate system. There is noneed to predict the necessary information to be acquired at the secondtiming in order to calculate the second target path. Since complicatedprediction processing is unnecessary, increase in computation load issuppressed. According to the first disclosure, as described above, it ispossible to increase the path-following performance with suppressingincrease in the computation load.

According to the second disclosure, the delay time from the first timingto the second timing is predetermined. In this case, the target pathcorrection processing is further simplified, which is preferable.

According to the third disclosure, the delay time from the first timingto the second timing corresponds to a time required for the target pathcalculation processing. In this case, it is possible to reduce influenceof the control delay caused by the target path calculation time.

According to the fourth disclosure, the new target path is determinedsuch that a certain section from the beginning of the new target pathoverlaps the previous target path. As a result, the new target path andthe previous target path are connected smoothly. Therefore,discontinuous change in a vehicle control amount is suppressed when thetarget path used for the vehicle travel control is switched. As aresult, sudden change and disturbance in vehicle behavior aresuppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram for explaining path-following control byan autonomous driving system according to a first embodiment of thepresent disclosure;

FIG. 2 is a conceptual diagram for explaining vehicle travel control inthe first embodiment of the present disclosure;

FIG. 3 is a conceptual diagram for explaining control delay due to atarget path calculation time in the first embodiment of the presentdisclosure;

FIG. 4 is a conceptual diagram showing difference in appearance of atarget path between a first coordinate system and a second coordinatesystem in the first embodiment of the present disclosure;

FIG. 5 is a conceptual diagram for explaining target path correctionprocessing in the first embodiment of the present disclosure;

FIG. 6 is a conceptual diagram for explaining the path-following controlby the autonomous driving system according to the first embodiment ofthe present disclosure;

FIG. 7 is a block diagram showing a configuration example of theautonomous driving system according to the first embodiment of thepresent disclosure;

FIG. 8 is a block diagram for explaining information acquisitionprocessing by the autonomous driving system according to the firstembodiment of the present disclosure;

FIG. 9 is a block diagram for explaining autonomous driving controlprocessing by the autonomous driving system according to the firstembodiment of the present disclosure;

FIG. 10 is a block diagram showing a functional configuration of apath-following control device of the autonomous driving system accordingto the first embodiment of the present disclosure;

FIG. 11 is a flow chart showing the path-following control by thepath-following control device according to the first embodiment of thepresent disclosure;

FIG. 12 is a conceptual diagram for explaining an updating cycle in asecond embodiment of the present disclosure;

FIG. 13 is a conceptual diagram for explaining a problem to be solved inthe second embodiment of the present disclosure;

FIG. 14 is a conceptual diagram for explaining target path calculationprocessing in the second embodiment of the present disclosure;

FIG. 15 is a block diagram showing a functional configuration of thepath-following control device of the autonomous driving system accordingto the second embodiment of the present disclosure;

FIG. 16 is a flow chart showing the path-following control by thepath-following control device according to the second embodiment of thepresent disclosure;

FIG. 17 is a block diagram showing a functional configuration of thepath-following control device of the autonomous driving system accordingto a third embodiment of the present disclosure; and

FIG. 18 is a flow chart showing the path-following control by thepath-following control device according to the third embodiment of thepresent disclosure.

EMBODIMENTS

Embodiments of the present disclosure will be described below withreference to the attached drawings.

1. First Embodiment 1-1. Outline of Path-Following Control by AutonomousDriving System

FIG. 1 is a conceptual diagram for explaining path-following control byan autonomous driving system according to the present embodiment. Theautonomous driving system is mounted on a vehicle 1 and controlsautonomous driving of the vehicle 1. The path-following control is akind of the autonomous driving control. More specifically, in thepath-following control, the autonomous driving system periodicallycalculates a target path TP for the vehicle 1, and controls travel ofthe vehicle 1 so as to follow the latest target path TP.

Here, let us define a vehicle coordinate system (X, Y). The vehiclecoordinate system is a relative coordinate system fixed to the vehicle 1and varies with motion of the vehicle 1. That is, the vehicle coordinatesystem is defined by a position and an orientation of the vehicle 1. Inthe example shown in FIG. 1, the X-direction is a front direction of thevehicle 1, and the Y-direction is a planar direction orthogonal to theX-direction. However, the vehicle coordinate system is not limited tothe example shown in FIG. 1.

The path-following control is performed based on the vehicle coordinatesystem. That is, the autonomous driving system periodically calculatesthe target path TP in the vehicle coordinate system. Then, theautonomous driving system controls travel of the vehicle 1 so as tofollow the latest target path TP. Controlling the travel of the vehicle1 so as to follow the target path TP is hereinafter referred to as“vehicle travel control”.

FIG. 2 is a conceptual diagram for explaining the vehicle travelcontrol. An example of a positional relationship between the vehicle 1and the target path TP in the vehicle coordinate system is shown in FIG.2. In the vehicle travel control, deviation of the vehicle 1 from thetarget path TP is controlled to be reduced in order to make the vehicle1 follow the target path TP. For that purpose, for example, parameterssuch as a lateral deviation Ed, an orientation angle difference θd, acurvature of the target path TP, and the like are taken intoconsideration. The lateral deviation Ed is an Y-direction deviation ofthe vehicle 1 from the target path TP. The orientation angle differenceθd is a difference in an angle of orientation between the vehicle 1 andthe target path TP. The autonomous driving system can perform thevehicle travel control based on the lateral deviation Ed, theorientation angle difference θd, the curvature of the target path TP,and the like.

The inventors of the present application have recognized the followingproblem with regard to the path-following control. That is, in thepath-following control, control delay may occur due to various factors.The control delay of the path-following control causes decrease inperformance of following the target path TP, which is not preferable.The various factors for the control delay include an informationcommunication time, a calculation processing time, an actuator responsetime, and so forth. Among them, what is considered to most contribute tothe control delay is a calculation time required for calculating thetarget path T, that is, a target path calculation time.

FIG. 3 is a conceptual diagram for explaining the control delay due tothe target path calculation time. At a first timing T1, the autonomousdriving system acquires information necessary for calculating the targetpath TP. The information necessary for calculating the target path TP ishereinafter referred to as “necessary information”. Then, the autonomousdriving system calculates a new target path TP based on the acquirednecessary information. It takes some time to calculate the target pathTP, and thus the calculation of the target path TP is completed at asecond timing T2 later than the first timing T1. A period from the firsttiming T1 to the second timing T2 corresponds to the target pathcalculation time.

In FIG. 3, a first position P1 is a position of the vehicle 1 at thefirst timing T1. A second position P2 is a position of the vehicle 1 atthe second timing T2. A first coordinate system (X1, Y1) is the vehiclecoordinate system at the first timing T1, that is, at the first positionP1. A second coordinate system (X2, Y2) is the vehicle coordinate systemat the second timing T2, that is, at the second position P2. The firstcoordinate system and the second coordinate system are different fromeach other by an amount corresponding to the target path calculationtime. Therefore, “appearance” of the target path TP differs between inthe first coordinate system and in the second coordinate system.

FIG. 4 shows difference in appearance of the target path TP between thefirst coordinate system and the second coordinate system. In FIG. 4, afirst target path TP1 represents the target path TP as seen from thefirst position P1, that is, the target path TP defined in the firstcoordinate system. On the other hand, a second target path TP2represents the target path TP as seen from the second position P2, thatis, the target path TP defined in the second coordinate system. Thefirst target path TP1 and the second target path TP2 are different fromeach other by an amount corresponding to the target path calculationtime.

Here, let us consider the vehicle travel control (see FIG. 2) by theautonomous driving system. The vehicle travel control based on a newtarget path TP can be naturally started after the new target path TP isdetermined, that is, after the second position P2 (the second timingT2). When the vehicle travel control is performed after the secondposition P2, higher control accuracy can be obtained by using the secondtarget path TP2 rather than the first target path TP1 to perform thevehicle travel control. However, it is impossible to directly calculatethe second target path TP2 from the necessary information. The reason isthat the necessary information is the information acquired at the firstposition P1 (first timing T1). What can be calculated by the use of thenecessary information acquired at the first position P1 is only thefirst target path TP1 defined in the first coordinate system.

When the first target path TP1 defined in the first coordinate system isused to perform the vehicle travel control, control error becomes largerand control accuracy becomes lower as compared with a case where thesecond target path TP2 defined in the second coordinate system is used.In other words, the performance of following the target path TP isdecreased. When the path-following performance of the autonomous drivingsystem is decreased, an occupant of the vehicle 1 feels senses ofanxiety and strangeness, which leads to decrease in confidence in theautonomous driving system.

In view of the above, the autonomous driving system according to thepresent embodiment performs “target path correction processing” thatcorrects the first target path TP1 to the second target path TP2. FIG. 5is a conceptual diagram for explaining the target path correctionprocessing in the present embodiment. As described above, the firsttarget path TP1 defined in the first coordinate system is calculatedfrom the necessary information acquired at the first position P1 (firsttiming T1). In the target path correction processing, the autonomousdriving system performs “coordinate transformation” from the firstcoordinate system to the second coordinate system to correct (convert)the first target path TP1 to the second target path TP2. Complicatedcomputation processing is unnecessary for the coordinate transformation,and it is possible to easily obtain the second target path TP2.

FIG. 6 shows in a summarized manner the path-following control by theautonomous driving system according to the present embodiment. At thefirst timing T1 (i.e. the first position P1), the autonomous drivingsystem acquires the necessary information. After that, at the secondtiming T2 (i.e. the second position P2), the autonomous driving systemcompletes calculation of the target path TP based on the necessaryinformation at the first position P1, that is, the first target pathTP1. Furthermore, the autonomous driving system performs the target pathcorrection processing to correct the calculated first target path TP1 tothe second target path TP2. Then, the autonomous driving system uses thesecond target path TP2 as the target path TP to perform the vehicletravel control such that the vehicle 1 follows the second target pathTP2.

1-2. Effects

As described above, the autonomous driving system according to thepresent embodiment performs the target path correction processing in thepath-following control. More specifically, the autonomous driving systemcorrects the first target path TP1 defined in the first coordinatesystem to the second target path TP2 defined in the second coordinatesystem. Influence of the control delay is reduced by the target pathcorrection processing. Therefore, when the second target path TP2 afterthe correction is used to perform the vehicle travel control, thecontrol error becomes smaller and the control accuracy becomes higher ascompared with the case where the first target path TP1 is used. In otherwords, the performance of following the target path TP is increased.When the path-following performance of the autonomous driving system isincreased, the senses of anxiety and strangeness of the occupant of thevehicle 1 are reduced, which contributes to increase in confidence inthe autonomous driving system.

It should be noted that, in the example shown in FIGS. 3 to 6, thetarget path calculation time is considered as a representative factorfor the control delay. However, the present embodiment is not limited tothat. For example, the control delay due to another factor (theinformation communication time, the actuator response time, and soforth) may be taken into consideration. Alternatively, a part of thetarget path calculation time may be taken into consideration. Whengeneralized, it is enough that the second timing T2 is delayed from thefirst timing T1 by a time corresponding to at least a part of thecontrol delay. Even when the second timing T2 is a little later than thefirst timing T1, the influence of the control delay is somewhat reducedby the target path correction processing according to the presentembodiment.

Moreover, complicated computation processing is unnecessary for thetarget path correction processing according to the present embodiment.It is possible to easily obtain the second target path TP2 by performingsimple coordinate transformation from the first coordinate system to thesecond coordinate system.

As a comparative example, let us consider the technique disclosed in theabove-mentioned Patent Literature 1. According to the technique,“prediction processing” is necessary for calculating the high-precisionsecond control command value. More specifically, the vehicle motionstate and the obstacle state detected by the sensors are used to predictfuture vehicle motion state and obstacle state. Then, the high-precisionsecond control command value is calculated based on the predicted futurevehicle motion state and obstacle state. However, such the predictionprocessing requires complicated computation processing, which causesincrease in computation load, computation time, and computationalresource.

On the other hand, according to the present embodiment, the predictionprocessing as in the comparative example is unnecessary. For example,there is no need to predict the necessary information to be acquired atthe future second timing T2 in order to calculate the high-precisionsecond target path TP2. It is the necessary information acquired at thefirst timing T1 that is used for calculating the target path TP. Thefirst target path TP1 is calculated from the necessary informationacquired at the first timing T1, and then the second target path TP2 isobtained by the simple coordinate transformation. Since complicatedprediction processing is unnecessary, increase in the computation load,computation time, and computational resource is suppressed.

As described above, the autonomous driving system according to thepresent embodiment can increase the path-following performance withsuppressing increase in the computation load. Hereinafter, a concreteconfiguration example of the autonomous driving system according to thepresent embodiment will be described.

1-3. Configuration Example of Autonomous Driving System

FIG. 7 is a block diagram showing a configuration example of theautonomous driving system 100 according to the present embodiment. Theautonomous driving system 100 is mounted on the vehicle 1 and controlsthe autonomous driving of the vehicle 1. More specifically, theautonomous driving system 100 is provided with a GPS (Global PositioningSystem) receiver 10, a map database 20, a surrounding situation sensor30, a vehicle state sensor 40, a communication device 50, a traveldevice 60, and a control device 70.

The GPS receiver 10 receives signals transmitted from a plurality of GPSsatellites and calculates a position and an orientation of the vehicle 1based on the received signals. The GPS receiver 10 sends the calculatedinformation to the control device 70.

Information indicating a boundary position of each lane on a map isbeforehand recorded in the map database 20. The boundary position ofeach lane is represented by a point group or a line group. The mapdatabase 20 is stored in a predetermined storage device.

The surrounding situation sensor 30 detects a situation around thevehicle 1. The surrounding situation sensor 30 is exemplified by a LIDAR(Laser Imaging Detection and Ranging), a radar, a camera, and the like.The LIDAR uses laser lights to detect a target around the vehicle 1. Theradar uses radio waves to detect a target around the vehicle 1. Thecamera images a situation around the vehicle 1. The surroundingsituation sensor 30 sends the detected information to the control device70.

The vehicle state sensor 40 detects a travel state of the vehicle 1. Thevehicle state sensor 40 is exemplified by a vehicle speed sensor, asteering angle sensor, a yaw rate sensor, a lateral acceleration sensor,and the like. The vehicle speed sensor detects a speed of the vehicle 1.The steering angle sensor detects a steering angle of the vehicle 1. Theyaw rate sensor detects a yaw rate of the vehicle 1. The lateralacceleration sensor detects a lateral acceleration of the vehicle 1. Thevehicle state sensor 40 sends the detected information to the controldevice 70.

The communication device 50 performs a V2X communication (i.e. avehicle-to-vehicle communication and a vehicle-to-infrastructurecommunication). More specifically, the communication device 50 performsa V2V communication (a vehicle-to-vehicle communication) with anothervehicle. In addition, the communication device 50 performs a V2Icommunication (a vehicle-to-infrastructure communication) with asurrounding infrastructure. Through the V2X communication, thecommunication device 50 can acquire information on an environment aroundthe vehicle 1. The communication device 50 sends the acquiredinformation to the control device 70.

The travel device 60 includes a steering device, a driving device, abraking device, a transmission, and so forth. The steering device turnswheels. The driving device is a power source that generates a drivingforce. The driving device is exemplified by an engine and an electricmotor. The braking device generates a braking force.

The control device 70 performs autonomous driving control that controlsthe autonomous driving of the vehicle 1. Typically, the control device70 is a microcomputer including a processor, a memory device, and aninput/output interface. The control device 70 is also called an ECU(Electronic Control Unit). The control device 70 receives a variety ofinformation through the input/output interface. The control device 70performs the autonomous driving control based on the receivedinformation.

More specifically, the control device 70 includes an informationacquisition unit 71 and an autonomous driving control unit 72 asfunctional blocks. These functional blocks are achieved by the processorof the control device 70 executing a control program stored in thememory device. The control program may be recorded on acomputer-readable recording medium. The information acquisition unit 71performs information acquisition processing. The autonomous drivingcontrol unit 72 performs autonomous driving control processing.

FIG. 8 is a block diagram for explaining the information acquisitionprocessing according to the present embodiment. In the informationacquisition processing, the information acquisition unit 71 acquiresinformation necessary for the autonomous driving control. Theinformation acquisition processing is repeatedly executed every certaincycle.

More specifically, the information acquisition unit 71 acquires, fromthe GPS receiver 10, position-orientation information 81 indicatingcurrent position and orientation of the vehicle 1.

Moreover, the information acquisition unit 71 reads the informationregarding lanes from the map database 20 to generate lane information82. The lane information 82 includes a geometry (i.e. position, shape,and orientation) of each lane on a map. Based on the lane information82, the information acquisition unit 71 can recognize lane merging, lanebranching, lane intersecting, and the like. Besides, the informationacquisition unit 71 can also calculate a lane curvature, a lane width,and the like based on the lane information 82.

Moreover, the information acquisition unit 71 generates surroundingsituation information 83 based on the information detected by thesurrounding situation sensor 30. The surrounding situation information83 includes target information regarding the target around the vehicle1. The target is exemplified by a white line, a roadside structure, asurrounding vehicle, and so forth.

Moreover, the information acquisition unit 71 generates vehicle stateinformation 84 based on the information detected by the vehicle statesensor 40. The vehicle state information 84 includes information on thespeed, the steering angle, the yaw rate, the lateral acceleration, andso forth of the vehicle 1.

Moreover, the information acquisition unit 71 receives deliveryinformation 85 through communication by the communication device 50. Thedelivery information 85 is information delivered from the infrastructureand the surrounding vehicle. The delivery information 85 is exemplifiedby roadwork section information, accident information, and so forth.

All of the position-orientation information 81, the lane information 82,the surrounding situation information 83, the vehicle state information84, and the delivery information 85 as exemplified above indicatedriving environment for the vehicle 1. Information indicating such thedriving environment for the vehicle 1 is hereinafter referred to as“driving environment information 80”. That is to say, the drivingenvironment information 80 includes the position-orientation information81, the lane information 82, the surrounding situation information 83,the vehicle state information 84, and the delivery information 85.

It can be said that the information acquisition unit 71 of the controldevice 70 has a function of acquiring the driving environmentinformation 80. As shown in FIG. 8, the information acquisition unit 71together with the GPS receiver 10, the map database 20, the surroundingsituation sensor 30, the vehicle state sensor 40, and the communicationdevice 50 constitute an “information acquisition device 110”. Theinformation acquisition device 110 as a part of the autonomous drivingsystem 100 performs the information acquisition processing describedabove.

FIG. 9 is a block diagram for explaining the autonomous driving controlprocessing according to the present embodiment. The autonomous drivingcontrol unit 72 performs autonomous driving control based on theabove-described driving environment information 80. In particular, theautonomous driving control unit 72 performs the path-following controlas a part of the autonomous driving control. In the path-followingcontrol, the autonomous driving control unit 72 calculates the targetpath TP of the vehicle 1 and controls travel of the vehicle 1 so as tofollow the target path TP. The travel of the vehicle 1 can be controlledby appropriately actuating the travel device 60.

The autonomous driving control unit 72 and the travel device 60constitute a “path-following control device 120”. The path-followingcontrol device 120 as a part of the autonomous driving system 100performs the path-following control. Hereinafter, the path-followingcontrol by the path-following control device 120 according to thepresent embodiment will be described in more detail.

1-4. Path-Following Control Device

FIG. 10 is a block diagram showing a functional configuration of thepath-following control device 120 according to the present embodiment.The path-following control device 120 includes a necessary informationacquisition unit 121, a target path determination unit 122, and avehicle travel control unit 126. The target path determination unit 122includes a target path calculation unit 123 and a target path correctionunit 124.

FIG. 11 is a flow chart showing the path-following control by thepath-following control device 120 according to the present embodiment.The path-following control by the path-following control device 120according to the present embodiment will be described with reference toFIGS. 10 and 11.

Step S10:

The necessary information acquisition unit 121 periodically acquiresnecessary information 90 through the information acquisition device 110.The necessary information 90 is information necessary for calculatingthe target path TP and is a part of the driving environment information80 described above. For example, the necessary information 90 includesthe position-orientation information 81, the lane information 82, thesurrounding situation information 83, and the delivery information 85. Atiming when the necessary information acquisition unit 121 acquires thenecessary information 90 is the first timing T1 (see FIGS. 3 and 6). Thenecessary information acquisition unit 121 acquires the necessaryinformation 90 and outputs the necessary information 90 to the targetpath determination unit 122 every first timing T1.

Step S20:

The target path determination unit 122 determines the target path TPbased on the necessary information 90 acquired at Step S10. Morespecifically, Step S20 includes the following Steps S30 to S50.

Step S30:

First, the target path calculation unit 123 performs target pathcalculation processing. More specifically, the target path calculationunit 123 calculates the target path TP based on the necessaryinformation 90 acquired at Step S10. Various methods of calculating thetarget path TP have been proposed. In the present embodiment, the methodof calculating the target path TP is not limited in particular. Thenecessary information 90 is one acquired at the first position P1, andthe target path TP calculated based on the necessary information 90 isthe first target path TP1 (see FIG. 4) defined in the first coordinatesystem. That is to say, the target path calculation unit 123 calculatesthe first target path TP1 based on the necessary information 90.

Step S40:

After the first target path TP1 is calculated, the target pathcorrection unit 124 performs the target path correction processing (seeFIG. 5). More specifically, the target path correction unit 124 performscoordinate transformation from the first coordinate system to the secondcoordinate system to correct (convert) the first target path TP1 to thesecond target path TP2 defined in the second coordinate system.

The first coordinate system is the vehicle coordinate system at thefirst timing T1 when the necessary information 90 is acquired. Thesecond coordinate system is the vehicle coordinate system at the secondtiming T2 later than the first timing T1. A difference between the firstcoordinate system and the second coordinate system can be calculated,for example, from the position-orientation information 81 at both thefirst timing T1 and the second timing T2. Alternatively, a differencebetween the first coordinate system and the second coordinate system canbe calculated based on the vehicle state information 84 (the vehiclespeed, the yaw rate, and the like) at the first timing T1 and a delaytime from the first timing T1 to the second timing T2.

It is preferable that the delay time from the first timing T1 to thesecond timing T2 is predetermined. In this case, setting informationindicating the delay time is beforehand stored in the memory device ofthe control device 70. The target path correction unit 124 can recognizethe delay time and the second timing T2 by reference to the settinginformation. When the delay time from the first timing T1 to the secondtiming T2 is predetermined, the target path correction processing isfurther simplified, which is preferable.

For example, the delay time from the first timing T1 to the secondtiming T2 is set to correspond to the target path calculation time (i.e.the time required for the target path calculation unit 123 to calculatethe target path TP). In this case, performing the target path correctionprocessing makes it possible to reduce influence of the control delaycaused by the target path calculation time.

Step S50:

The target path determination unit 122 sets the second target path TP2obtained at Step S40 as the target path TP. Then, the target pathdetermination unit 122 outputs the target path TP to the vehicle travelcontrol unit 126.

Step S60:

The vehicle travel control unit 126 performs the vehicle travel controlthat controls the travel of the vehicle 1 so as to follow the targetpath TP (see FIGS. 2 and 6). More specifically, based on the parameterssuch as the lateral deviation Ed, the orientation angle difference θd,the curvature of the target path TP and the like, the vehicle travelcontrol unit 126 calculates a vehicle control amount for reducing thedeviation of the vehicle 1 from the target path TP. Then, the vehicletravel control unit 126 actuates the travel device 60 in accordance withthe calculated vehicle control amount.

For example, the travel device 60 includes a power steering device (EPS:Electric Power Steering) for turning wheels of the vehicle 1. It ispossible to turn the wheels by performing driving control of a motor ofthe power steering device. The vehicle travel control unit 126calculates a target steering angle required for following the targetpath TP. In addition, the vehicle travel control unit 126 acquires anactual steering angle from the vehicle state information 84. Then, thevehicle travel control unit 126 calculates a motor current command valueaccording to a difference between the actual steering angle and thetarget steering angle, and drives the motor in accordance with the motorcurrent command value. In this manner, the vehicle travel control isachieved.

1-5. Modification Example

The delay time from the first timing T1 to the second timing T2 is notnecessarily limited to the target path calculation time. For example,the delay time from the first timing T1 to the second timing T2 may beset in consideration of the information communication time, the actuatorresponse time, and the like.

When the delay time from the first timing T1 to the second timing T2 isthe target path calculation time, the delay time may be actuallymeasured, instead of giving a predetermined value as the delay time.More specifically, at the above-described Step S30, the target pathcalculation unit 123 measures a processing time of the target pathcalculation processing and outputs the measurement result to the targetpath correction unit 124. The target path correction unit 124 canrecognize the second timing T2 and the second coordinate system based onthe measurement result.

2. Second Embodiment 2-1. Outline

The necessary information 90 necessary for calculating the target pathTP is periodically acquired and updated. Every time the necessaryinformation 90 is updated, the target path TP is determined and updatedas well. In the following description, a suffix “k−1” represents theprevious and a suffix “k” represent the latest.

FIGS. 12 and 13 show an example of updating of the necessary information90 and the target path TP. At the previous first timing T1(k−1), theprevious necessary information 90 is acquired. At the previous secondtiming T2(k−1), the previous target path TP(k−1) is obtained. At thefirst timing T1(k), the new necessary information 90 is acquired. At thesecond timing T2(k), the new target path TP(k) is obtained. That is, thetarget path TP is updated.

During a period from the first timing T1(k) to the second timing T2(k),the new target path TP(k) is under calculation and not yet determined.Therefore, during the period from the first timing T1(k) to the secondtiming T2(k), the vehicle travel control is performed based on theprevious target path TP(k−1). At the second timing T2(k), the new targetpath TP(k) is determined. After that, the vehicle travel control can beperformed based on the new target path TP(k).

Here, let us consider a case where the previous target path TP(k−1) andthe new target path TP(k) are irrelevant to each other and notcontinuous, as shown in FIG. 13. In this case, the vehicle controlamount in the vehicle travel control changes discontinuously at a timingwhen the target path TP is switched. The discontinuous change in thevehicle control amount causes sudden change and disturbance in vehiclebehavior and thus gives the occupant of the vehicle 1 senses ofstrangeness and anxiety. In view of the above, the second embodiment ofthe present disclosure proposes target path calculation processing thatcan suppress the discontinuous change in the vehicle control amount.

FIG. 14 is a conceptual diagram for explaining the target pathcalculation processing in the second embodiment. According to the secondembodiment, the new target path TP(k) is determined so as to partiallyoverlap the previous target path TP(k−1). More specifically, as shown inFIG. 14, the new target path TP(k) is determined such that a certainsection from the beginning of the new target path TP(k) overlaps theprevious target path TP(k−1). The certain section includes at least asection from the first position P1(k) at the first timing T1(k) to thesecond position P2(k) at the second timing T2(k).

Due to the target path calculation processing described above, the newtarget path TP(k) and the previous target path TP(k−1) are connectedsmoothly. In particular, the new target path TP(k) overlaps the previoustarget path TP(k−1) in the section from the first position P1(k) to thesecond position P2(k). Therefore, at the second position P2(k), there isno discontinuity between the previous target path TP(k−1) and the newtarget path TP(k). Thus, the discontinuous change in the vehicle controlamount is suppressed when the target path TP is switched. As a result,sudden change and disturbance in the vehicle behavior are suppressed.

2-2. Path-Following Control Device

FIG. 15 is a block diagram showing a functional configuration of thepath-following control device 120 according to the second embodiment. Anoverlapping description with the first embodiment shown in FIG. 10 willbe omitted as appropriate. The path-following control device 120according to the second embodiment includes a target path determinationunit 122A in place of the target path determination unit 122. The targetpath determination unit 122A includes a target path calculation unit123A.

FIG. 16 is a flow chart showing the path-following control by thepath-following control device 120 according to the second embodiment. Anoverlapping description with the first embodiment shown in FIG. 11 willbe omitted as appropriate. In the second embodiment, Step S20 isreplaced by Step 520A.

Step 520A:

The target path determination unit 122A determines the target path TPbased on the necessary information 90 acquired at Step S10. Morespecifically, Step 520A includes the following Step 530A.

Step S30A:

The target path calculation unit 123A performs the target pathcalculation processing based on the necessary information 90 and theprevious target path TP(k−1). More specifically, the target pathcalculation unit 123A calculates the new target path TP(k) such that acertain section from the beginning of the new target path TP(k) overlapsthe previous target path TP(k−1). The certain section includes at leastthe section from the first position P1(k) to the second position P2(k).

The target path determination unit 122A outputs the target path TP(k)calculated at Step 530A to the vehicle travel control unit 126. Thetarget path TP is switched from the previous target path TP(k−1) to thenew target path TP(k), and the vehicle travel control unit 126 startsthe vehicle travel control based on the new target path TP(k). At theswitching timing, discontinuous change in the vehicle control amount issuppressed. As a result, sudden change and disturbance in the vehiclebehavior are suppressed.

3. Third Embodiment

A third embodiment of the present disclosure is a combination of thefirst embodiment and the second embodiment. An overlapping descriptionwith the first embodiment or the second embodiment will be omitted asappropriate.

FIG. 17 is a block diagram showing a functional configuration of thepath-following control device 120 according to the third embodiment. Thepath-following control device 120 according to the third embodimentincludes a target path determination unit 122B in place of the targetpath determination unit 122. The target path determination unit 122Bincludes a target path calculation unit 123B and a target pathcorrection unit 124B.

FIG. 18 is a flow chart showing the path-following control by thepath-following control device 120 according to the third embodiment. Inthe third embodiment, Step S20 is replaced by Step 520B.

Step 520B:

The target path determination unit 122B determines the target path TPbased on the necessary information 90 acquired at Step S10. Morespecifically, Step 520B includes the following Steps 530B to 550B.

Step 530B:

The target path calculation unit 123B performs the target pathcalculation processing based on the necessary information 90 and theprevious target path TP(k−1). More specifically, the target pathcalculation unit 123B calculates the new target path TP(k) such that acertain section from the beginning of the new target path TP(k) overlapsthe previous target path TP(k−1). The certain section includes at leastthe section from the first position P1(k) to the second position P2(k).The target path TP(k) calculated at Step 530B is the first target pathTP1(k) defined in the first coordinate system.

Step 540B:

After the latest first target path TP1(k) is calculated, the target pathcorrection unit 124B performs the target path correction processing (seeFIG. 5). More specifically, the target path correction unit 124Bperforms coordinate transformation from the first coordinate system tothe second coordinate system to correct the first target path TP1(k) tothe second target path TP2(k) defined in the second coordinate system.

Step 550B:

The target path determination unit 122B sets the second target pathTP2(k) obtained at Step 540B as the target path TP. Then, the targetpath determination unit 122B outputs the target path TP to the vehicletravel control unit 126.

According to the third embodiment, both of the effects by the firstembodiment and the effects by the second embodiment are obtained.

What is claimed is:
 1. An autonomous driving system that controls avehicle, the autonomous driving system comprising: a processorprogrammed to periodically acquire information that is necessary forcalculating a target path, wherein a first timing is a timing when theprocessor acquires the information, a first coordinate system is avehicle coordinate system fixed to the vehicle at the first timing, asecond coordinate system is a vehicle coordinate system fixed to thevehicle at a second timing later than the first timing, and theprocessor is further programmed to: calculate a first target pathdefined in the first coordinate system, based on the informationacquired at the first timing; correct the first target path defined inthe first coordinate system to a second target path defined in thesecond coordinate system by performing coordinate transformation fromthe first coordinate system to the second coordinate system; calculate avehicle control amount for reducing a deviation of the vehicle from thesecond target path; and control an actuator of the vehicle in accordancewith the calculated vehicle control amount.
 2. The autonomous drivingsystem according to claim 1, wherein the deviation of the vehicle fromthe second target path includes a lateral deviation of the vehicle fromthe second target path.
 3. The autonomous driving system according toclaim 1, wherein the deviation of the vehicle from the second targetpath includes a difference in an angle of orientation between thevehicle and the second target path.
 4. A method for controlling avehicle with a processor, the method comprising: periodically acquiringinformation that is necessary for calculating a target path, wherein afirst timing is a timing when the processor acquires the information, afirst coordinate system is a vehicle coordinate system fixed to thevehicle at the first timing, a second coordinate system is a vehiclecoordinate system fixed to the vehicle at a second timing later than thefirst timing, and the method further comprises: calculating a firsttarget path defined in the first coordinate system, based on theinformation acquired at the first timing; correcting the first targetpath defined in the first coordinate system to a second target pathdefined in the second coordinate system by performing coordinatetransformation from the first coordinate system to the second coordinatesystem; calculating a vehicle control amount for reducing a deviation ofthe vehicle from the second target path; and controlling an actuator ofthe vehicle in accordance with the calculated vehicle control amount. 5.A non-transitory computer readable recording medium storing a programthat causes a processor to execute: periodically acquiring informationthat is necessary for calculating a target path, wherein a first timingis a timing when the processor acquires the information, a firstcoordinate system is a vehicle coordinate system fixed to the vehicle atthe first timing, a second coordinate system is a vehicle coordinatesystem fixed to the vehicle at a second timing later than the firsttiming, and the program causes the processor to further execute:calculating a first target path defined in the first coordinate system,based on the information acquired at the first timing; correcting thefirst target path defined in the first coordinate system to a secondtarget path defined in the second coordinate system by performingcoordinate transformation from the first coordinate system to the secondcoordinate system; calculating a vehicle control amount for reducing adeviation of the vehicle from the second target path; and controlling anactuator of the vehicle in accordance with the calculated vehiclecontrol amount.